Method for manufacturing partially acylated regenerated cellulose foil or fiber

ABSTRACT

Partly acetylated regenerated cellulose films or fibers are manufactured by first swelling them in a concentrated and waterfree acetic acid solution of an alkali metal acetate at a temperature ranging between 50* and 140* C. Immediately thereafter and without drying the swelled films or fibers are esterified by an acetic acid anhydride solution containing alkali metal acetate at a temperature ranging between 100* and 170* C.

ited States atem Tammela et a1.

[ Mar. 14, 1972 [54] METHOD FOR MANUFACTURING PARTIALLY ACYLATEDREGENERATED CELLULOSE FOIL OR FIBER Inventors: Viljo Tammela, Helsinki;Olli Turunen,

Porvoo; both of Finland Assignee: Neste 0y, Helsinki, Finland Filed:Nov. 14, 1968 Appl. No: 775,952

Foreign Application Priority Data Nov. 17. 1967 Finland ..3106/67 U.S.Cl..1l7/1l8,8/121,1l7/60, 1 17/ 144 Int. (1. ..B44d 51/2, D06m 13/20 Fieldof Search ..8/120, 121; 117/60, 144.5, 117/ 144, l 18 References CitedUNITED STATES PATENTS 4/1936 McKee et a1. ..8/121 UX 2,772,944 12/1956Allewelt ..8/121 2,780,511 2/1957 Takagi 1.8/1 2 1 3,215,490 11/1965Fraizy et al. ..8/121 FOREIGN PATENTS OR APPLICATIONS 353,978 8/1931Great Britain ....8/l2l 448,063 6/1936 Great Britain ....8/l2l 750,7026/1956 Great Britain..... ....8/l21 930,208 7/1963 Great Britain ..8/121Primary Examiner-William D. Martin Assistant Examiner-M. R. LusignanAttorney-Richards & Geier 1 1 ABSTRACT Partly acetylated regeneratedcellulose films 0r fibers are manufactured by first swelling them in aconcentrated and water-free acetic acid solution of an alkali metalacetate at a temperature ranging between 50 and 140 Immediatelythereafter and without drying the swelled films or fibers are esterifiedby an acetic acid anhydride solution containing alkali metal acetate ata temperature ranging between 100 and 1 70 C.

1 Claims, No Drawings METHOD FOR MANUFACTURING PARTIALLY ACYLATEDREGENERATED CELLULOSE FOIL OR FIBER The present invention concerns amethod for manufacturing partially acylated cellulose foil or fiber inwhich the foil or fiber which is to be esterified is at first swollen atelevated temperature and subsequently esterified, whereupon the productis washed and dried.

Since regenerated cellulose presents drawbacks as low wet strength andbrown discoloration at high temperatures, methods have been developed inwhich the properties of regenerated cellulose foil or fiber are improvedby means of partial acylation. By such methods the objectionablecharacteristics of regenerated cellulose foil or fiber can indeed beeliminated because partially acylated regenerated cellulose foil orfiber has good heat resistance and high wet strength. In the acylatingmethods of previous art initial treatment of the regenerated cellulosefoil or fiber has been accomplished by first swelling the foil or fiberin aqueous solutions of salts, after which step it has been necessary todry the swollen foil or fiber prior to esterification and only afterthis has the acylating process been performed with acid anhydrides. Ifacid esterification catalysts have been used as components in the acidanhydride solution, it has furthermore been necessary prior toesterification to remove by washing the salts absorbed by the foil andfibers during the swelling process. As a consequence of thecircumstances mentioned, the acylating methods employed up to date havein fact been slow and complicated. In addition, partial depolymerizationand discoloration of the cellulose may occur.

The object of the present invention is to afford a method for acylatingregenerated cellulose foil or fiber which is superior to previousmethods in speed and simplicity. The invention is accordingly mainlycharacterized in that swelling of the foil or fiber is accomplished in asubstantially water-free aliphatic carboxylic acid solution containingsalt of an alkali metal and an aliphatic carboxylic acid and that theproduct thus obtained is immediately esterified in a manner previouslyknown in itself in a solution of the anhydride of a low-molecularcarboxylic acid which contains salt of an alkali metal and an aliphaticcarboxylic acid. Since it is not necessary in a method according to theinvention to dry the swollen foil or fiber because the foil or fiber isswollen in a substantially water-free swelling solution, nor to wash itbecause esterification may be accomplished immediately after swellingwithout causing any damage to the foil or fiber, it follows that amethod according to the invention surpasses any previous methods in thespeed and simplicity with which it can be carried out.

it has been found that alkali metal salts of low-molecular aliphaticcarboxylic acids, solved in aliphatic carboxylic acids, are mosteffective for use as cellulose-swelling agents in the method formanufacturing partially acylated regenerated cellulose concerned here.Alkali metal acetates solved in acetic acid have been found to be themost efficient ones among them.

The composition of the acid anhydride solutions used in the method mayvary considerably. It is possible to use for acylating agent merely theanhydride of some low-molecular carboxylic acid or a mixture of these.With increasing molecular size of the anhydrides increasingly softproducts are obtained, e.g., compared to the use of acetic acidanhydride alone.

For use as reaction accelerators in the esterifying solution the samesalts are most effective as are used for bloating agents in thepretreatment.

It is possible to use as raw material e.g., unsoftened regeneratedcellulose foil or fiber,

Pretreatment is accomplished by immersing the regenerated cellulose foilor fiber into a swelling bath at elevated temperature, e.g., at 50-l40C.

The pretreated product thus obtained is immediately immersed, withoutintervening drying, into the esterifying solution at elevatedtemperature, e.g., at lO-l 70 C.

After completed esterification the acylated foil is washed with aceticacid and with water. Fiber may also be washed with water alone, wherebythe luster characteristic of the fibers can be dulled.

The foils or fibers may be bleached upon completed washing if necessary,

If a more flexible product is desired, the partially acylated productmay also be immersed into a solution containing a softener prior todrying.

Drying is accomplished by the usual method employed for regeneratedcellulose.

By a method according to the invention partially acylated regeneratedcellulose foil or fiber with good heat resistance and possessing wetstrength is obtained.

The dry tensile strengths of the foils were determined according to theASTM D 1708-59 method. The determination of wet tensile strengthdiffered from the said method in that the test specimens were keptimmersed in water at room temperature for 20 hours prior to the tensiletest. The average dry and wet strengths of the original regeneratedcellulose foils were 1,300 and 200 kp/cm. The determinations of heatresistance were carried out according to the ASTM D 1637-61 method,stating as the heat resistance of the foil the temperature at which theelongation of the specimen was 2 percent of its original length. Theheat resistance of the regenerated cellulose foil, according to the ASTMD 1637-61 method, was 200 C.

The brown discoloration of the foils was studied by keeping the samplesfor 1 hour at 210 C. and, subsequently, determin ing their transparencywith a spectrophotometer according to the ASTM D 1746-62 method. Thetransparencies were stated in percent at the wavelengths of 400 and 550mu. Prior to the heat treatment, the transparencies of the original aswell as the partially regenerated cellulose foil amounted to 84-85percent at 400 mu and to 87-88 percent at 550 mu. The transparency ofthe original regenerated cellulose foil after heating for 1 hour at 200C. was 67-70 percent at 550 my. and 40-42 percent at 400 mu.

The method according to the invention is illustrated by a few examplesin the following.

EXAMPLE 1 Acetic anhydride Potassium acetate 98 parts by weight 2 partsby weight Acetylation was followed by washing for 30 seconds in aceticacid at room temperature, whereupon the foil was furthermore washed withwater, and dried. The clear foil which was obtained had the followingproperties:

Thickness 37 ,4 Acetyl content 2471 Heat resistance 200 C.

Transparency after the discoloration test, at 400 my 74-75 percent, at550 mp. 84-85 percent Wet tensile strength Dry tensile strength EXAMPLE2 The test was performed as in Example 1, but the esterifying solutionhad a different composition, which was:

Acetic anhydride Potassium acetate Acetic acid 92 parts by weight 5parts by weight 3 parts by weight The end product had the followingproperties:

Thickness 37 Acetyl content 23% Heat resistance 200 C.

Transparency after the discoloration test, at 400 mp. 73-74 percent, at550 mp 84-85 percent Wet tensile strength Dry tensile strength EXAMPLE 3The procedure applied in the test differed from that in Example only inrespect of the esterifying solution, which was:

Acetic anhydride Potassium acetate Acetic acid 85 parts by weight 5parts by weight l0 parts by weight The foil which was obtained had thefollowing properties:

Thickness Acetyl content Heat resistance Transparency after thediscoloration test, at 400 mp. 60-70 percent, at 550 mp 80-82 percentWet tensile strength Dry tensile strength EXAMPLE 4 The test wasperformed as in Example 1, but a regenerated cellulose fiber bundle wasused instead of regenerated cellulose foil. In addition, the acetylatingsolution had a composition differing from that mentioned above, and itwas:

304 kp/cm. 956 ltplcm,

Acetic anhydride Potassium acetate Acetic acid EXAMPLES The test wasperformed in Example I, but the composition of the esterifying solutionwas different; it was:

Acetic anhydridc Potassium acetate 95 parts by weight 5 parts by weightAfter acetylation for 1 minute and after the subsequent washings, thefoils had the following properties:

Thickness Acetyl content Hcitt tcststance Transparency after thediscoloration test, at 400 mu 76-77 percent, at 550 mp. 83-86 percentWet tensile strength Dry tensile strength EXAMPLE 6 The test wasperformed as in Example 1, but the composition of the esterifyingsolution was different from that mentioned above; it was:

Acetic anhydridc Butyric anhydride Potassium acetate Thickness 4.5;.

Acclyl content 28.4 Butyryl content 5.2% Heat resistance 200 C.

Transparency after the discoloration test, at 400 mp. 76 percent, at 550mp 86 percent wet tensile strength Dry tensile strength The dryelongation was found to be 15 percent, whereas the dry elongation ofmerely acetylated foils is in the order of 10-12 percent; the additionof butyryl content thus exerts a plasticizing effect on the foils.

EXAMPLE 7 The test was performed as in Example l, but commercialregenerated cellulose foil (plasticizer content, about 10 percent) wasused instead of isotropic foil. The esterifying solution had thefollowing composition:

Acetic anhydride Potassium acetate After acetylation for 1 minute andsubsequent washings. the foils had the following properties:

Thickness 28;; (Original. 30p.) Acetyl content 30% Heat resistance2(l0"C. (Original, 200" C.)

Transparency after the discoloration test:

at 400 my. at 550 mp Wet tensile strength in the machine direction 435kp/cm. (Original, 225 kp/cm?) Wet tensile strength across the machinedirection 250 kp/cm. (Original. l40 kplcmf) Dry tensile strength in themachine direction Dry tensile strength across the machine direction tilSlip/cm. (Original, 500 lip/cm) Comparison of the acetyl contents of thefoils obtained in Examples 2 and 3 reveals that the acetic acid presentin the esterifying solution retards the reaction rate. This detrimentcan be avoided in a continuous process either by removing the aceticacid from the esterifying solution or by adding to it salt used toaccelerate the reaction, whereby the acylating rate can be maintainedvirtually constant.

it is seen from the examples presented that in a method according to theinvention the acetylating process takes less than 5 minutes, exclusiveof potential bleaching, washing with water and drying.

The wet strength of the partially esterified (acetyl content, 30-35percent) regenerated cellulose foil (400 kp/cm?) is markedly better thanthat of the merely regenerated cellulose foil (200 kp/cm?) and nearlyequals that of cellulose acetate foils (450 kp/cm. The heat resistanceof partially acetylated regenerated cellulose foil is 200 C. if theacetyl content is 33 percent. Such partially esterified cellulose foilis not soluble in a cellulose solvent such as Cadoxene solution nor incellulose acetate solvents such as acetone, 2-methoxy ethanol aceticacid or chloroform.

We claim:

I. The method for manufacturing partly acetylated regenerated cellulosefilm or fibers, which comprises swelling the film or fibers in asubstantially water-free acetic acid solution of an alkali metal acetateat a temperature of 50l40 C. and immediately thereafter esterifying themwithout drying by an acetic acid anhydride solution containing alkalimetal acetate at a temperature of l-l70 C. and then washing and dryingthem.

